帮忙看看， 没有答案的，马上就要考了

4. Although the turtle has been toothless for more than 150 million years, in some contemporary turtle species the moderately sharp and jagged edges of their horny jaws function for teeth.

A. their horny jaws function for teeth

B. its horny jaws function for teeth

C. its horny jaws function as do teeth

D the horny jaws function as teeth do

E the horny jaws function as teeth

我觉得是C